Triangle tube dual wall brazed plate heat exchanger started leaking

Geode

Good morning,
Sadly my heat exchanger has begun leaking after 8 years in use (not at any of the four connection ports). Is 8 years a decent run for this type of exchanger? I've also found that the exchanger has been discontinued since August (with no suggested replacement) and it appears triangle tube is no longer making dual wall brazed plate heat exchangers? I can't locate any dual wall units on their website/online. Model is FHETTP5-14DW. Definitely looking for advice on this, and suggestions on getting a suitable replacement. I'm fairly handy and installed our system from a design I received from Northeast radiant technology in 2012. I believe NRT has been out of business for quite a while now unfortunately. Thanks, Steve

GGross

A lot of factors will determine the life cycle of a heat exchanger, most of all water quality. Triangle Tube purchased those heat exchangers from AIC, same place they got the heat exchangers for their boilers. I don't see that same model on the current list price sheets, my recommendation to get something really close, would be to contact an AIC distributor, or you could try them direct though I doubt they do one off sales

hot_rod

Does it need to be double walled? Are you running ethylene glycol on one side?
plenty of companies build plate heat exchangers, should be easy to cross it over to any brand.

GGross

I have found the plate heat exchangers from badger pipe to be pretty good, and pretty inexpensive
https://badger-pipe.com/collections/water-to-water-brazed-plate-exchanger

Geode

GGross said:

A lot of factors will determine the life cycle of a heat exchanger, most of all water quality. Triangle Tube purchased those heat exchangers from AIC, same place they got the heat exchangers for their boilers. I don't see that same model on the current list price sheets, my recommendation to get something really close, would be to contact an AIC distributor, or you could try them direct though I doubt they do one off sales

hot_rod said:

Does it need to be double walled? Are you running ethylene glycol on one side?
plenty of companies build plate heat exchangers, should be easy to cross it over to any brand.

Double wall is required by code in my area (central Illinois in 2014 ) when there is the possibility for cross contamination. I'm using a Polaris water heater for potable and radiant heat with the exchanger isolating the two (plain water on both sides) Hindsight probably been better off with a small boiler setup. House is 650 sq. ft. so the heating load is pretty small. Sounds like single wall is fine for most of the country? Just to confirm, this is the AIC you mentioned https://aicheatexchangers.com/l-line-brazed-plate-heat-exchangers/
Thanks for the help

mattmia2

Look at your water quality, specifically chlorides and compare to the specs for the HX. You might want to find an alloy that is more resistant to your water.

Alan (California Radiant) Forbes

Double-wall heat exchangers used to be required here, but then it was dropped about 10 years ago and it was greatly celebrated as heat transfer, as you might expect is much better with single wall.

Check with your local building inspection office to see if double-wall is still required.

hot_rod

Are you on a public water system? If so you have a backflow device that prevents you from contaminating the city water. So worse case boiler water gets into your water.

I would check local code I don’t believe the 2022 code requires double walk, unless your AHJ gas an amendment?

Geode

hot_rod said:

Are you on a public water system? If so you have a backflow device that prevents you from contaminating the city water. So worse case boiler water gets into your water.

I would check local code I don’t believe the 2022 code requires double walk, unless your AHJ gas an amendment?

Checked with building safety, and yes they are fine with a single wall hx! Huge thanks to everyone, so glad to have learned that and the possibility to improve efficiency would be welcome. For the sizing, that is a bit beyond me. As I understand a single wall transfers heat more efficiently, this will allow for me to down size the heat exchanger?

hot_rod

If you want the long answer on how to size a HX, here it is

https://www.caleffi.com/sites/default/files/file/idronics_29_na.pdf

The online sizing programs are easy to use, an example included in this journal. No harm ion a bit of oversize, other than cost.

Geode

Thanks for the links.

hot_rod said:

If you want the long answer on how to size a HX, here it is

https://www.caleffi.com/sites/default/files/file/idronics_29_na.pdf

The online sizing programs are easy to use, an example included in this journal. No harm ion a bit of oversize, other than cost.

Thanks for the links. My primary loop with circulator is attached to the hot/cold water heater space heater taps. Water pressure is ~ 50 psi. I understand that some pressure drop through the HX is desirable to facilitate heat transfer. Sizing up the HX the pressure drop decreases accordingly, any ballpark figures you might throw out?

Additional information fwiw.
Supply temperature is 135F, total max radiant load is 45k btu, max radiant temperature is 120F delivered via Tekmar 356 injection mixing setup.

Looking at a 20 or 30 plate HX from badger.

mattmia2

does it still run at 135 on a dhw call or does it increase the swt?

hot_rod

Are they 5x12” dimension? Without running all the numbers I suspect a 5x12- 20 plate would cover it

What is the dimension of the old one. A similar physical size in single wall should perform a bit better

Geode

hot_rod said:

Are they 5x12” dimension? Without running all the numbers I suspect a 5x12- 20 plate would cover it

What is the dimension of the old one. A similar physical size in single wall should perform a bit better

The old unit is 5" x 21" with 14 plates (total surface area of 1470 sq. inch.)
The badger HX's are all 5" x 12", the 20 plate(1200 sq. inch), 30 plate (1800 sq. inch)
Not sure if looking at the surface area is relevant due to the single walls improved heat transfer, but the old HX does fall between the 20 and 30 plate Badger HX's in surface area.
Thank you

Geode

mattmia2 said:

does it still run at 135 on a dhw call or does it increase the swt?

The low setpoint for the water heater is typically set to 135F. Domestic utilizes a mixing valve set to120F. There is no priority setup between domestic and heating. If we draw hot domestic water just before the supply temperature hits the 135F setpoint the supply will dip below 135F until the water heater gets going. Not sure if that answers your question? Water heater is 34 gallons,100,000 btu so recovers quickly.

Looked briefly at our water quality report and didn't find a mention of chlorides. We get our water from the Mahomet aquifer system which is considered one of the best in the Midwest for water quality. I imagine that is relative though.
Thanks

hot_rod

The only way to give you the best answer it to run the numbers. The online calculators are free. You need at least 3 inputs, temperatures and flows, it calculates the rest and gives you a size, and sq" of surface.

I've heard grossly oversizing reduces channel velocity and lowers transfer somewhat.

Geode

hot_rod said:

The only way to give you the best answer it to run the numbers. The online calculators are free. You need at least 3 inputs, temperatures and flows, it calculates the rest and gives you a size, and sq" of surface.

Hi Bob,
I've heard grossly oversizing reduces channel velocity and lowers transfer somewhat.

Attached a few screen grabs from my calculations, thanks for the encouragement. I plugged in 7.5 GPM for the A side rate. The flow rate will be variable as my system is using injection mixing to set the heat output. The A side GPM is probably the rate required during maximum btu output?

My injection pump can supply up to 20 GPM, ideally a lower rate would be preferred? I arbitrarily used 7.5 for my calculations,

What is a reasonable oversurface percent to shoot for?

Thanks very much

Geode

hot_rod said:

The only way to give you the best answer it to run the numbers. The online calculators are free. You need at least 3 inputs, temperatures and flows, it calculates the rest and gives you a size, and sq" of surface.

I've heard grossly oversizing reduces channel velocity and lowers transfer somewhat.

Hi Bob,
I've attached a few screenshots of my calculations. Thanks for the encouragement. My primary circulator is controlled by a tekmar 356 injection controller. The pump is capable of 0 to 20 GPM. I arbitrarily used 7.5 GPM in the A side of the calculator. This is the GPM required to get full BTU on the B side?
Should I be looking at different GPM on the A side?

What type of numbers should I be looking at for oversurface percent?

Thanks so much

hot_rod

That size is close but with your inputs it gets you 29,000, you need 45,000?
if so, more flow, higher temperature, or more surface area.
I would guess you could flow more gpm on the A side?  Pull the pump curve, ideally you want to run mud curve, maybe 19- 12 gpm on that circulator?  If so, try 10 gpm on the A side, see if that get you 45,000 btu/ hr

Geode

hot_rod said:

That size is close but with your inputs it gets you 29,000, you need 45,000?
if so, more flow, higher temperature, or more surface area.
I would guess you could flow more gpm on the A side?  Pull the pump curve, ideally you want to run mud curve, maybe 19- 12 gpm on that circulator?  If so, try 10 gpm on the A side, see if that get you 45,000 btu/ hr

I need 30k, which is not only the heat load estimated by NRT but also what I have observed over the last couple of years of operation.

A google search suggested an oversurface percent of up to 50% to offset and loss's due to fouling etc.
Thanks

hot_rod

Ideally you keep the HX clean instead of taking the "fouling" hit. The hydronic side should not foul if you have good fill water.

The potable water side of the HX should have two iso purge valves so it can be delimed occasionally if you have hard water? No different than a tankless water heater, combi, heat exchanger of any kind.

I like this valve in a threaded version on both potable water connection. A tankless delime kit simplifies de-liming.

If the HX is fouled performance drops, efficiency goes down, fuel costs go up, if that matters?

My gut tells me a 5x12- 20 will work, upsize if you want. Probably don't need a 30 plate, but if the price is right and there is nothing between a 20 and 30 at the site...

Sizing software is intended to give you the best size based on accurate inputs, an engineered solution.
Most online plate HX sales give very vague BTU numbers, really not based on your exact application. So buyers tend to buy more than they need.

Geode

hot_rod said:

Ideally you keep the HX clean instead of taking the "fouling" hit. The hydronic side should not foul if you have good fill water. The potable water side of the HX should have two iso purge valves so it can be delimed occasionally if you have hard water? No different than a tankless water heater, combi, heat exchanger of any kind. I like this valve in a threaded version on both potable water connection. A tankless delime kit simplifies de-liming. If the HX is fouled performance drops, efficiency goes down, fuel costs go up, if that matters? My gut tells me a 5x12- 20 will work, upsize if you want. Probably don't need a 30 plate, but if the price is right and there is nothing between a 20 and 30 at the site... Sizing software is intended to give you the best size based on accurate inputs, an engineered solution. Most online plate HX sales give very vague BTU numbers, really not based on your exact application. So buyers tend to buy more than they need.

Hi Bob, our water quality is very good, no possibility for fouling (I do flush the system every year). Thanks for the insights!
Steve

Geode

Hi Bob,
Picked up a 30 plate 5 x 12 HX. noticed some rust/sludge in the radiant circuit while reworking some of the piping. The only ferrous parts are two cast iron alpha pumps. HX is stainless. Could replacing the cast iron pumps with SS models take care of things, should I be looking at a Dirtmag and or cleaning chemicals/flushing? I'll be doing some research online but I'm running out of time with winter approaching.
Best
Steve

All pex tubing does have an oxygen barrier.

hot_rod

All ferrous metals will corrode or rust in the presence of O2 in a hydronic system. It can be minimized, but not stopped completely. Everything  in that circuit would need to be non ferrous. Is there an expansion tank in the loop, that would need to be a radiant specific or stainless

O2 barriers slow the oxygen ingress, but cannot stop it completely.  A squirt of hydronic conditioner can help slow corrosion, they have oxygen inhibitors blended in.

Geode

Expansion tank is radiant specific (radiant extrol with plastic liner). Would a magnetic filter be worthwhile in addition to the hydronic conditioner? Thank you so very much for the info.

Geode

@GGross Went with a hx from badger pipe, happy with the quality/function, thanks for the suggestion. @hot_rod A 5x12 30 plate hx doing fine for us at temperatures of -12F.....ouch. Added some hydronic conditioner, thanks for the advice. Happy holidays everyone.
Cheers